I have a laptop on which I have two drives with separate Windows XP installs, one barebones for music production, the other "normal" Windows XP with Office etc. (unfortunately the bios won't give a boot disk choice).
Normally I would be presented with two Windows XPs on booting. Selecting the second one would get me into the "normal" installation on disk 1 (C:). Selecting the first in boot order would give me D:\ (disk 2) with the barebones XP.
However, I installed Windows 7 Home onto disk 1 (C:), but there were no dual boot options anymore, even though I installed DualBoot Pro and added Windows XP disk D:.
The options now show up, but selecting Windows XP just turns into a reboot back to where I started.